Title:  

Tidally Induced Parametric Excitation in Dwarf Spheroidal Galaxies



Jean_Julien Fleck
Ecole Normale Superieure, Paris



Abstract:
 
        Due to their high velocity dispersion, the dwarf spheroidal (dS)
galaxies of the Local Group are often described as the closest, smallest
and amongst the densest objects containing Dark Matter of all the
Universe. But what if there was a more conventional explanation to these
properties?

        The tidal MW-dS interaction on a star in the dS is well described
by the Mathieu equation -- which explains a parametric oscillator's
behavior. For most orbits there are a range of orbital parameters where
resonance can occur and inflate the dS (in size and velocity dispersion)
where classical tidal arguments would predict stablity. A tidally induced
parametric excitation can thus substantially inflate the velocity
dispersion and dramatically confuse estimates of dS properties which
assume virial equilibrium.